8.1
The momentum of the object does not change when only the mass is changed. The momentum is changed much longer if the force is applied for a longer amount of time.

8.2
When mass is changed it also changes the kinectic energy and speed. Speed alters the kinectic energy

8.3
If a momentum decreases the other one must increase becuase the forces are always equal but opposite. The sum of the impulses of the balls has to equal zero because of the previously mentioned concept.